Origin

An ancient word that has relatives in most northern European languages. The root may also be the source of Latin currere ‘to run’ ( see cursor). Horse racing has given numerous expressions to the language. The saying horses for courses is from the idea that each racehorse is suited to one particular racecourse and will do better on that than on any other. A. E. T. Watson's The Turf in 1891 was the first to record this observation, which he describes as ‘a familiar phrase on the turf’. The underlying idea of straight from the horse's mouth is that the best way to get racing tips is to ask a horse directly. One of the first examples comes from a 1913 edition of the Syracuse Herald: ‘Lionel hesitated, then went on quickly. “I got a tip yesterday, and if it wasn't straight from the horse's mouth it was jolly well the next thing to it.”’ People often say something like, ‘Oh, wild horses wouldn't…’, meaning that nothing could persuade them to do that particular thing, not realizing the horrific reference—it comes from the old custom of executing criminals by tying each of the four limbs to four horses and then urging the horses on, tearing the person into four pieces. To flog a dead horse is to waste energy on a lost cause or a situation that cannot be altered. Dead horse used to be workmen's slang for work that was charged for before it was done: to work or work for a dead horse was to do work that you had already been paid for.

An early form of the proverb you can lead a horse to water but you can't make him drink was ‘They can but bringe horse to the water brinke, But horse may choose whether that horse will drinke’ ( 1602). The horse chestnut was formerly said to be a remedy for chest diseases in horses, and its name is a translation of Latin Castanea equina. In horsefly (Late Middle English), horseradish (late 16th century), and similar terms horse implies ‘large of its kind’. See also dark, easel, equestrian, gift